* Pass various options to the worker so that flags like -K or -j work

in multi-user Nix (NIX-72).
* Client/worker: exchange a protocol version number for future
  compatibility.

src/libexpr/primops.cc

@@ -773,7 +773,6 @@ static Expr prim_listToAttrs(EvalState & state, const ATermVector & args)
       if (matchAttrs(evaledExpr, attrs)){
         Expr e = evalExpr(state, makeSelect(evaledExpr, toATerm("attr")));
         string attr = evalStringNoCtx(state,e);
-        ATerm value;
         Expr r = makeSelect(evaledExpr, toATerm("value"));
         res.set(toATerm(attr), makeAttrRHS(r, makeNoPos()));
       }
@@ -783,7 +782,7 @@ static Expr prim_listToAttrs(EvalState & state, const ATermVector & args)
     } // for
     return makeAttrs(res);
   } catch (Error & e) {
-    e.addPrefix(format("while calling listToAttrs "));
+    e.addPrefix(format("in `listToAttrs':\n"));
     throw;
   }
 }

src/libstore/remote-store.cc

@@ -53,18 +53,24 @@ RemoteStore::RemoteStore()
     from.fd = fdSocket;
     to.fd = fdSocket;
 
-    
     /* Send the magic greeting, check for the reply. */
     try {
         writeInt(WORKER_MAGIC_1, to);
-        writeInt(verbosity, to);
         unsigned int magic = readInt(from);
         if (magic != WORKER_MAGIC_2) throw Error("protocol mismatch");
+
+        unsigned int daemonVersion = readInt(from);
+        if (GET_PROTOCOL_MAJOR(daemonVersion) != GET_PROTOCOL_MAJOR(PROTOCOL_VERSION))
+            throw Error("Nix daemon protocol version not supported");
+        writeInt(PROTOCOL_VERSION, to);
         processStderr();
+
     } catch (Error & e) {
         throw Error(format("cannot start worker (%1%)")
             % e.msg());
     }
+
+    setOptions();
 }
 
 
@@ -154,6 +160,19 @@ RemoteStore::~RemoteStore()
 }
 
 
+void RemoteStore::setOptions()
+{
+    writeInt(wopSetOptions, to);
+    writeInt(keepFailed, to);
+    writeInt(keepGoing, to);
+    writeInt(tryFallback, to);
+    writeInt(verbosity, to);
+    writeInt(maxBuildJobs, to);
+    writeInt(maxSilentTime, to);
+    processStderr();
+}
+
+
 bool RemoteStore::isValidPath(const Path & path)
 {
     writeInt(wopIsValidPath, to);

src/libstore/remote-store.hh

@@ -77,6 +77,8 @@ private:
     void forkSlave();
     
     void connectToDaemon();
+
+    void setOptions();
 };
 
 

src/libstore/worker-protocol.hh

@@ -5,8 +5,11 @@
 namespace nix {
 
 
-#define WORKER_MAGIC_1 0x6e697864
-#define WORKER_MAGIC_2 0x6478696e
+#define WORKER_MAGIC_1 0x6e697863
+#define WORKER_MAGIC_2 0x6478696f
+
+#define PROTOCOL_VERSION 0x101
+#define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 
 
 typedef enum {
@@ -28,6 +31,7 @@ typedef enum {
     wopExportPath,
     wopImportPath,
     wopQueryDeriver,
+    wopSetOptions,
 } WorkerOp;
 
 

src/nix-worker/nix-worker.cc

@@ -414,6 +414,19 @@ static void performOp(Source & from, Sink & to, unsigned int op)
         
         break;
     }
+
+    case wopSetOptions: {
+        keepFailed = readInt(from) != 0;
+        keepGoing = readInt(from) != 0;
+        tryFallback = readInt(from) != 0;
+        verbosity = (Verbosity) readInt(from);
+        maxBuildJobs = readInt(from);
+        maxSilentTime = readInt(from);
+        startWork();
+        stopWork();
+        break;
+    }
+            
             
     default:
         throw Error(format("invalid operation %1%") % op);
@@ -437,14 +450,19 @@ static void processConnection()
     /* Exchange the greeting. */
     unsigned int magic = readInt(from);
     if (magic != WORKER_MAGIC_1) throw Error("protocol mismatch");
-    verbosity = (Verbosity) readInt(from);
     writeInt(WORKER_MAGIC_2, to);
 
+    writeInt(PROTOCOL_VERSION, to);
+    unsigned int clientVersion = readInt(from);
+
     /* Send startup error messages to the client. */
     startWork();
 
     try {
 
+        /* If we can't accept clientVersion, then throw an error
+           *here* (not above). */
+
         /* Prevent users from doing something very dangerous. */
         if (geteuid() == 0 &&
             querySetting("build-users-group", "") == "")